"This isn’t just aviation licences in isolation. This is being looked at as a huge topic involving the acceptance of professional qualifications across many fields. Accountancy, Law, etc."
Jonty is correct - and one of the worst places is the USA - every profession (lawyers, undertakers, hairdressers, taxi drivers, engineers...) tries to build licence walls in every US state to protect themselves - and they have a great deal of influence on law-makers. That's why you pay a realtor 2x or 3x as much in the USA as you would in many European countries.